Class AB amplifier having cascode stage with filter for improving linearity

Abstract

The present invention provides a class AB amplifier, wherein the class AB amplifier includes a cascode stage with a filter and an output stage. The cascode stage with the filter is arranged for receiving an input signal to generate a first driving signal and a second driving signal, wherein the filter filters the input signal to generate an filtered input signal, and at least one of the first driving signal and the second driving signal is generated according to the filtered input signal. The output stage is coupled to the cascode stage, and is arranged for generating an output signal according to the first driving signal and the second driving signal.

What is claimed is: 
     
       1. A class AB amplifier, comprising:
 a cascode stage with a filter, for receiving an amplified input signal from a previous stage to generate a first driving signal and a second driving signal; wherein the filter filters the amplified input signal to generate a filtered input signal, and at least one of the first driving signal and the second driving signal is generated according to the filtered input signal; and 
 an output stage, coupled to the cascode stage, for generating an output signal according to the first driving signal and the second driving signal. 
 
     
     
       2. The class AB amplifier of  claim 1 , wherein the filter is a high-pass filter. 
     
     
       3. The class AB of  claim 1 , wherein both the first driving signal and the second driving signal comprise AC component of the amplified input signal. 
     
     
       4. The class AB amplifier of  claim 1 , wherein the cascode stage comprises:
 a P-type transistor, wherein the filtered input signal is inputted into a gate electrode of the P-type transistor to generate the first driving signal at a source electrode of the P-type transistor. 
 
     
     
       5. The class AB amplifier of  claim 4 , wherein the filter is a high-pass filter, and the filter comprises:
 a capacitor, coupled between the amplified input signal and the gate electrode of the P-type transistor; and 
 a resistor, coupled between a bias voltage and the gate electrode of the P-type transistor. 
 
     
     
       6. The class AB amplifier of  claim 4 , wherein the output stage comprises a P-type output transistor and an N-type output transistor connected in cascode, wherein the P-type output transistor receives the first driving signal, and the N-type output transistor receives the amplified input signal serving as the second driving signal, to generate the output signal. 
     
     
       7. The class AB amplifier of  claim 1 , wherein the cascode stage comprises:
 an N-type transistor, wherein the filtered input signal is inputted into a gate electrode of the N-type transistor to generate the second driving signal at a source electrode of the N-type transistor. 
 
     
     
       8. The class AB amplifier of  claim 7 , wherein the filter is a high-pass filter, and the filter comprises:
 a capacitor, coupled between the amplified input signal and the gate electrode of the N-type transistor; and 
 a resistor, coupled between a bias voltage and the gate electrode of the N-type transistor. 
 
     
     
       9. The class AB amplifier of  claim 7 , wherein the output stage comprises a P-type output transistor and an N-type output transistor connected in cascode, wherein the N-type output transistor receives the second driving signal, and the P-type output transistor receives the amplified input signal serving as the first driving signal, to generate the output signal. 
     
     
       10. The class AB amplifier of  claim 1 , wherein the cascode stage comprises:
 a P-type transistor, wherein the filtered input signal is inputted into a gate electrode of the P-type transistor to generate the first driving signal at a source electrode of the P-type transistor; and 
 an N-type transistor, wherein the filtered input signal is further inputted into a gate electrode of the N-type transistor to generate the second driving signal at a source electrode of the N-type transistor. 
 
     
     
       11. The class AB amplifier of  claim 10 , wherein the filter comprises:
 a first capacitor, coupled between the amplified input signal and the gate electrode of the P-type transistor; 
 a first resistor, coupled between a bias voltage and the gate electrode of the P-type transistor; 
 a second capacitor, coupled between the amplified input signal and the gate electrode of the N-type transistor; and 
 a second resistor, coupled between a bias voltage and the gate electrode of the N-type transistor. 
 
     
     
       12. The class AB amplifier of  claim 10 , wherein the output stage comprises a P-type output transistor and an N-type output transistor connected in cascode, wherein the P-type output transistor receives the first driving signal, and the N-type output transistor receives the second driving signal, to generate the output signal. 
     
     
       13. The class AB amplifier of  claim 1 , wherein the class AB amplifier is a static class AB amplifier. 
     
     
       14. A class AB amplifier, comprising:
 an input stage, for receiving an input signal to generate an amplified input signal; 
 a cascode stage with a filter, coupled to the input stage, for receiving the amplified input signal to generate a first driving signal and a second driving signal; wherein the filter filters the amplified input signal to generate a filtered input signal, and at least one of the first driving signal and the second driving signal is generated according to the filtered input signal; and 
 an output stage, coupled to the cascode stage with the filter, for generating an output signal according to the first driving signal and the second driving signal. 
 
     
     
       15. The class AB amplifier of  claim 14 , wherein the filter is a high-pass filter. 
     
     
       16. The class AB of  claim 14 , wherein both the first driving signal and the second driving signal comprise AC component of the amplified input signal. 
     
     
       17. The class AB amplifier of  claim 14 , wherein the cascode stage comprises:
 a P-type transistor, wherein the filtered input signal is inputted into a gate electrode of the P-type transistor to generate the first driving signal at a source electrode of the P-type transistor. 
 
     
     
       18. The class AB amplifier of  claim 17 , wherein the output stage comprises a P-type output transistor and an N-type output transistor connected in cascode, wherein the P-type output transistor receives the first driving signal, and the N-type output transistor receives the second driving signal, to generate the output signal.